The present invention relates to a high purity ZrB2 powder having a purity of 99.9 wt % or higher, and the manufacturing method thereof.
ZrB2 (Zirconium Diboride) is a substance that has similar physical properties as GaN, and the lattice constant and coefficient of thermal expansion are both approximate. The electrical conductivity is high, and the specific thermal conductivity also shows a high value comparable to metallic molybdenum. In recent years, the use of ZrB2 as a substrate for blue laser semiconductors utilizing the foregoing properties is being studied.
The crystal structure of ZrB2 is an alternately overlapping structure of a hexagonal net-like boron layer and zirconium metal layer. It is necessary to grow single crystals in the foregoing usage as a substrate, and the high frequency induction heating FZ method (Floating Zone Method) is generally used for manufacturing this single crystal substrate (refer to Non-Patent Document 1).
Nevertheless, in the manufacture of a single crystal substrate with the FZ method, a major problem has been discovered. The problem is that the purity of the ZrB2 powder raw material to be used in sintering is inferior and it is difficult to manufacture large single crystals, whereby the manufacturing efficiency is extremely inferior.
As conventional technology, for instance, as shown in Patent Document 1, proposed is a manufacturing method of a high purity ZrB2 sintered body of adding to the ZrB2 powder an organosilicon compound capable of primarily transforming into SiC based on pyrolysis, molding the resultant product, and thereafter performing pressureless sintering thereto.
Nevertheless, Patent Document 1 relates to cutting tools and thermal engine components utilizing properties such as high hardness, high heat resistance, high corrosion resistance and the like, and the purity of ZrB2 was essentially left out of consideration.
Further, a manufacturing method of a mixed powder containing zirconium oxide and boride, and a compound sintered body containing such powder has been proposed (refer to Patent Document 2). Patent Document 2 is also for use in carbide tools and high-temperature structures, and similarly does not give consideration to demands of high purity materials.
In light of the foregoing circumstances, there is an article concerning the manufacture of a high purity ZrB2 powder (refer to Non-Patent Document 2). Nevertheless, the manufacturing method of this high purity ZrB2 powder is based on the reduction of ZrO2 by B4C and C, and the inclusion of large amounts of C cannot be avoided.
Further, as shown in Table 1 of Non-Patent Document 2, the purity level is ZrO2: 99.0%, B4C: 97%, and large amounts of Si, Fe and the like are mixed in as impurities, and it cannot be said that sufficient purity was realized for obtaining the high purity ZrB2 powder required in manufacturing a single crystal substrate.    [Non-Patent Document 1] The Institute of Electronics, Information and Communication Engineers, IEICE Technical Journal, Shigeki Otani “Present Situation of ZrB2 Substrate Manufacture”, pages 17 to 19, vol. 102, No. 114 (2002)    [Non-Patent Document 2] China Building Materials Academy, Beijing 100024, China, H. ZHAO and 2 others “PREPARATION OF ZIRCONIUM BORIDE POWDER” pages 573 to 576, (1995), 5th Ins Symp Ceram. Mater. Compon. Engines 1994    [Patent Document 1] Japanese Patent Laid-Open Publication No. 63-297273    [Patent Document 2] Japanese Patent Laid-Open Publication No. S63-282165